This invention relates to liquid flow rate measuring and liquid sampling methods and apparatuses and more particularly to methods and apparatus which are adjustable to provide for measurement and/or sampling of liquid streams including streams that are flowing at a low rate or are shallow.
One class of flow meter utilizes a movable gate or obstruction in a flow stream to alter the flow so as to enable easier measurement of flow rate and one type of sampler uses an obstruction and fixed flow bed to provide a location of relatively still and deep water from which to draw a representative sample.
One prior art flow measuring device for altering the flow stream to be measured utilizes a buoyant weir plate in the stream of a liquid. The tip of the buoyant weir includes a graduated depth gauge so that as the buoyant weir is lifted by its buoyancy and the rate of flow, the depth can be read on its graduated scale and a calculation of flow rate made therefrom. This type of device is disclosed in U.S. Pat. No. 3,087,335.
This type of flow measuring device has several disadvantages such as: (1) it is not as precise in its measurements as desired; and (2) it requires a visual on-sight reading and manual entry of depth data to obtain flow rates.
Another prior art flow device is disclosed in U.S. Pat. No. 4,200,120. This device controls gas flow with two movable valves in series in a gas stream, such as may be used to mix air with fuel in an internal combustion engine. The first valve is located upstream from the second valve and is varied in orientation in the stream such that the pressure difference between the pressure upstream of the first valve and the pressure between the two valves is kept constant. This is accomplished by extracating the pressure of the two chambers and sending them to a device which measures and amplifies any difference.
The result of this difference is sent to a feedback control mechanism and then to a valve opening mechanism which changes the position of the first valve to maintain the pressure differential between the two chambers. The position of the first valve is used to calculate the velocity of the gas.
This type of apparatus has a disadvantage in that it is complicated and not easily adaptable to a wide range of liquid flow rates because of the fixed position of the second valve and the location of the conduits connecting the chambers.